1. Field of the Invention
This invention relates to doctor blade holders, and is concerned in particular with an improved design that simplifies holder manufacturing, assembly, installation and maintenance.
2. Description of the Prior Art
Many roll cleaning and sheet shedding applications on papermaking machines and other web handling applications involve blade support devices commonly referred to as doctor blade holders for supporting blades such as doctor blades, creping blades and scraping blades etc.
Certain prior art doctor blade holders include a top plate (to which a doctor blade is joined), a bottom plate, and a mounting and adjustment assembly between the top and bottom plates. The bottom plate is mounted on a doctorback, which is a heavy-duty beam that spans the paper machine width. The rear portion of a doctor blade is received into the doctor blade holder that supports the blade in a pre-determined position relative to a surface to be cleaned. The doctor blade holder works in concert with the doctor blade to apply the working edge of the doctor blade, found on the blade's front portion, to an adjacent moving surface such as a roll.
FIG. 1 for example, shows a prior art doctoring apparatus 10 that is adjacent to the surface of a roll 12. The roll rotates about an axis A1, and the doctoring apparatus includes a doctorback 14 that is rotatable about an axis A2, which is parallel to the axis A1. A doctor blade holder 16 is shown supported on a beam 18, which forms part of the doctorback. The doctor blade holder 16 includes has top plate 20 and a bottom plate 22 that are joined by a mounting and adjustment assembly. A doctor blade 24 is received within a lower jaw opening 26 on the underside of the top plate 20.
With further reference to FIG. 2, the mounting and adjustment assembly includes a plurality of top plate brackets 28 and a plurality of bottom plate brackets 30 that are mutually joined together by a pivot rod 32. The mounting and adjustment assembly also includes a loading tube 34 and an unloading tube 36 that may each be alternately increased or decreased in size by adjusting an amount of fluid within each tube to effect a limited rotation of the top plate with respect to the axis A3 that is the central axis of the pivot rod 32. This limited rotation permits the doctor blade 24 to engage the roll 12 to effect doctoring, or to disengage the roll 12. A piston/cylinder unit 38 acts via a crank arm 40 to rotate the doctorback 14 about axis A2 in order to provide gross positioning of the doctor blade 24 near and away from the roll surface.
Doctor blade holders are typically assemblages of several discrete components, many of which (such as the brackets 28 and 30) are duplicated within the assembly dozens or scores of times, and must be riveted or otherwise fastened to the plates 20 and 22 respectively. This multiplicity of components has allowed holder manufacturers to custom-build holders to match the custom-built paper machines. These multiple repeating components, however, require substantial assembly time, which increases holder cost and opportunities for assembly errors.
Other prior art doctor blade holders, such as disclosed in U.S. Pat. No. 6,447,646, include an extruded or pultruded holder frame 40 that is pivotally mounted to an extruded or pultruded bearer 42 via a jointed bearing assembly 44 as shown in FIG. 3. The jointed bearing assembly 44 includes a joint sleeve 46 (e.g., in holder frame 40) that couples with a unified axle 48 (e.g., in the bearer 42). A doctor blade 50 is coupled to a blade holder 52, which is attached to the holder frame 40. Loading devices 54 and 56 apply positive and negative loading forces to the doctor blade 50 with respect to the roll 58. Separating the holder frame 40 from the bearer 42, however, requires sliding the holder frame 40 and the bearer 42 with respect to one another along the full elongated dimension of the doctoring apparatus, which may be a several or more meters in width. This may not only be awkward and/or impractical, but it may further require that the doctoring apparatus be moved to a more spacious location. U.S. Patent Applications Publication Nos. 2006/0180291 and 2006/0289141, as well as U.S. Pat. No. 6,942,734 also disclose doctor blade holder systems that include integrally formed mounting elements that extend along the elongated dimension of the doctor blade.
Further prior art blade holder systems, such as for example disclosed in U.S. Patent Application Publication No. 2006/0054293, include a base plate 60 and a cover plate 62 having a finger device 64 that receives a scrapping blade 66 as shown in FIG. 4. The base plate 60 and cover plate 62 are pivotally coupled together by a bearing tube 68 mounted on the based plate 60, which is received within a square tube 70 mounted to the underside of the cover plate 62. The square tube 70 is disclosed to be installed in segments in a direction perpendicular to the plane of the drawing in order to impair the resilience of the cover plate 62 as little as possible. The rotational position of the cover plate 62 with respect to the base plate 60 is adjustable by the inflation/deflation of an air pressure hose 72 in cooperation with a spring 74. Separating the cover plate 62 from the base plate 60, however, requires sliding the cover plate 62 and the base plate 60 with respect to one another along the full elongated dimension of the doctoring apparatus, which may be a several or more meters in width.
An objective of the present invention is to provide an improved holder design that greatly reduces the number of components and the assembly time, while providing means for quick and reliable in-situ disassembly for maintenance and repair of new and existing systems.